1. Field of the Invention
This invention relates to a base station transmission-reception apparatus for use with an automotive telephone system and a portable telephone system (cellular system), and more particularly to a base station transmission-reception apparatus wherein interference of the same frequency as another cell is reduced using a sector antenna.
2. Description of the Related Art
A base station transmission-reception apparatus for a cellular system which handles a large number of radio stations is disclosed in, for example, Moriji Kuwabara, "Digital Mobile Communication," Science Newspaper Company. The base station transmission-reception apparatus disclosed in the document includes, as shown in FIG. 1, a base station antenna 1, a common amplifier 2 for collectively amplifying the power of a plurality of radio channels, and a modulator-demodulator 3 for modulating and demodulating a digital signal.
A control center which communicates with the base station transmission-reception apparatus includes an exchange 103 including a circuit control apparatus 104. Where communications are performed using a digital signal, a speech processing apparatus 101 and a base station control apparatus 102 are provided between the base station and the control center. However, they may be provided in the base station and the control center.
A base station transmission-reception apparatus in urban areas which have a large amount of traffic adopts a sector cell configuration wherein a directional antenna is employed for base station antenna 1 in order to assure a high frequency utilization efficiency. A three-sector configuration wherein one cell is divided by 120 degrees into three sectors and a six-sector configuration wherein one cell is divided by 60 degrees into six sectors are in practically use. The base station antenna 1 includes two antennae including an antenna for common transmission and reception and the other for diversity reception antenna for each sector.
The common amplifier 2 includes a transmission amplifier 4 and a pair of outdoor reception amplifiers 2,008 and 2,009 for each sector as shown in FIG. 2. The transmission amplifier 4 includes a transmission common amplifier 41 for amplifying a transmission signal input from a modulator-demodulator and outputting the thus amplified signal to an outdoor reception amplifier 2,008 by way of an antenna feeder 2,001, a power separator-filter 42 for filtering a reception signal from the outdoor reception amplifier 2,008 and outputting the thus filtered signal as a reception signal to the modulator-demodulator, and power separator-filter 43 for filtering a reception signal from outdoor reception amplifier 2,009 and outputting the thus filtered signal as a diversity reception signal to the modulator-demodulator.
The transmission-reception antenna 2,006 is connected to the outdoor reception amplifier 2,008, and the diversity reception antenna 2,007 is connected to the outdoor reception amplifier 2,009.
The outdoor reception amplifier 2,008, to which the transmission-reception antenna 2,006 is connected, includes a power separator-filter 2,002, a reception common amplifier 5, and a duplexer 6 for using the transmission-reception antenna 2,006 commonly for transmission and reception. The outdoor reception amplifier 2,009, to which the diversity reception antenna 2,007 is connected includes a power separator-filter 2,003, a reception common amplifier 2,009, and a reception filter 2,005.
As shown in FIG. 3, the modulator-demodulator 3 provided in the base station 3,000 includes RF distribution composition sections 7 provided individually for the sectors, a transmitter-receiver 8, and an interface 3,006 which serves as a transmission line to and from a control center 9. An interface 3,006 is connected to control a bus control circuit 10, a supervision control circuit 3,006, a BCE interface 3,007 and a timing supply circuit 3,008 by way of a bus.
The transmitter-receiver 8 includes TRX sections 3,004 installed for individual carrier frequencies and a shelf control section 3,003 and performs .pi./4QPSK modulation/demodulation, demultiplexing of a TDMA (Time Division Multiple Access) signal, demultiplexing of an information channel and a control channel, and other necessary operations.
The base station 3,000 includes, in addition to the modulator-demodulator 3, an amplifier 3,001 for amplifying transmission and reception signals to be sent to and received from the RF distribution composition sections 7, a base station control apparatus 3,010 for controlling the inside of the base station, a synchronization dependent exchange 3,009, and other necessary apparatus not shown.
A synchronization dependent exchange 3,012, a base station control apparatus 3,015, a speech processing apparatus 3,014 and an exchange 3,013 are provided in the control center 9, and the control center 9 is connected to a fixed network 3,011 by way of the exchange 3,013.
In a conventional cellular system having the construction described above, the base station antennae 1, common amplifiers 2, RF distribution composition sections 7 of modulator-demodulator 3 and TRX sections 3,004 in transmitter-receiver 8 are provided independently for the individual sectors. When a mobile unit during communication moves from one sector to another sector, the control center is informed, and hand-over processing wherein channel allocation is performed again by the exchange of the control center is required.
In a cellular system, channel allocation is required in order to efficiently re-use a plurality of channels allocated to the system. While a fixed allocation system wherein an available frequency is allocated for each cell and each sector (for example, a system wherein a frequency is re-used for each 3 sectors and 7 cells) is in practical use, in order to further raise the frequency utilization efficiency, a dynamic channel allocation system wherein interference conditions of channels are monitored by individual base stations to allocate an available channel is investigated at present.
Further, in addition to the TDMA/FDMA (Frequency Division Multiple Access) systems wherein a channel is distinguished by a frequency and a time slot, a CDMA (Code Division Multiple Access) system wherein a frequency is commonly used by all channels and a channel is distinguished in accordance with a spreading code is in practical use.
In a base station transmission-reception apparatus of the sector cell configuration of the type described above, since the transmitter-receiver used for each sector is fixed, there is a disadvantage in that, if a mobile unit moves from one sector to another sector, hand-over processing described above is required, resulting in an equivalent increase in the load to the control center. Further, there is another disadvantage in that a number of transmitter-receivers corresponding to the maximum traffic must be prepared for each sector.
With a conventional base station transmission-reception apparatus, particularly where the dynamic channel allocation system or the CDMA system is employed, the frequency utilization efficiency can be enhanced by increasing the number of sectors. However, as the number of sectors is increased, the disadvantages described above becomes even more pronounced.
Further, since a conventional base station transmission-reception apparatus includes a radio section for each sector, it is economically disadvantageous in that, as the number of channels per apparatus increases, more time is required for operations for adjustment and inspection.